Electrosurgery is the use of high frequency electrical current (usually radio frequencies of 1 to 5 megahertz) for cutting tissues and for also causing coagulation of hemostasis of tissues. It is also used as an exclusive technique in transurethral resections (TUR's) and laparoscopic tubal ligations. The basic mechanisms responsible for either the cutting or coagulation of the tissues is the production of heat either at the immediate site of the electrical arc or in adjacent tissue. This heat is the result of the unique properties of high frequency current with the current density and duration of current flow being recognized as determining the amount of heat generated in the tissue. Two basic wave forms are used: an undamped sinusoidal wave form found most useful for cutting tissue; and a series of highly damped sinusoidal waves found most effective in coagulating tissue. High frequencies are used in eletrosurgery because they will not stimulate the patient's muscles and they are easily coupled into the tissues.
Although many standards exist for electrosurgical units, the following have been proposed as appropriate approximations of the characteristics of electrosurgical units. The units are normally capable of delivering at least 150 watts of cutting power into 500 ohms of resistance. Coagulation power is at least 50 watts. The load impedance is normally in the range between 100 and 1000 ohms, the impedance varying depending upon the type of tissue (bone, skin, fat or muscle,) location, (surface or underlying tissue), and local blood circulation. The amount of current varies with the load impedance, whether cutting or coagulation is being done, and the type of surgery involved and can range from 2000 ma. for cutting TUR down to 240 ma. for general coagulation use. Electrosurgery is discussed in greater detail in volume 2 of "Health Devices", Issues Nos. 8-9, 11, and 12 (June-October 1973), a monthly publication by "Emergency Care Research Institute of Philadelphia, Pennsylvania."
Electrosurgery, like all other uses of electricity, requires a complete circuit for current to flow. The circuit begins at the high frequency generator, goes through an active cable and an active electrode to the patient (who constitutes the load) and returns to the generator by way of a grounding pad electrode and a cable attached therebetween. The ability of electrosurgical high frequency current to affect tissue depends on the current density, the greater the current density the greater the heating effect. If the electrode is small, the heating will be concentrated near the electrode's point of contact with a patient. Obviously this is desired with the active electrode in order to cause the cutting or coagulation of tissue. However, no tissue heating is desired near the point where the current leaves a patient to return to the electrosurgical unit. Thus the return electrode or grounding pad electrode should provide a low impedance and a low current density path for the return current. If the grounding pad electrode does not provide a low impedance path for the return current, the current will seek alternate means to return to the electrosurgical unit and complete the circuit. Usually the alternate paths provide high current density and tissue heating and burns on the patient are the likely result. Thus, good patient contact with a return electrode having very low current density is necessary to avoid the alternate current pathways. Similarly, burns can occur at the return electrode if there is inadequate patient contact with the electrode to disperse the current. Thus, the use of an adequate grounding pad electrode is necessary in order to assure safe, burn-free electrosurgery.
Most hazards of electrosurgical units involve failure of the electro-mechanical connection between the grounding pad electrode and electrosurgical units or inadequate patient contact with the grounding pad electrode. Grounding pad electrodes, therefore, should conform to the patient, resist patient scratching, and should have connectors that are rugged and able to withstand routine use.
Because the body has an extremely low impedance to surface current, the grounding pad electrode can be located almost anywhere on the body. Nevertheless, in general the larger the electrode, the flusher the electrode is to the skin, and the closer the electrode is placed to the operating site, the lower will be the amount of required electrosurgical power. Generally, the prior art electrodes are applied around a curved area (e.g., the arm or leg) or comprise a large metal plate that is placed beneath a large flat area of the patient (e.g., the back or buttocks). However, in many operations (such as a chest operation) the patient is placed on his side and the arms are used for blood transfusions and sampling and for a central vascular pressure monitor and the thighs may be used for connections to a heart lung machine. Thus there is very little area left on the patient on which to attach a conventional grounding pad electrode.
There are numerous electrodes in the prior art and those presently known to the applicant include the electrodes disclosed in the following U.S. patents: Patrick, U.S. Pat. No. 3,848,600; Johnson U.S. Pat. No. 3,830,229; Anderson U.S. Pat. No. 3,683,923; Estes U.S. Pat. No. 3,601,126; Bolduc U.S. Pat. No. 3,543,760; Bolduc U.S. Pat. No. 3,642,008; Bolduc U.S. Pat. No. 3,699,968; Bolduc U.S. Pat. No. 3,720,209; Sessions U.S. Pat. No. 3,741,219; Kawaguchi U.S. Pat. No. 3,685,645; Blackett U.S. Pat. No. 3,662,757; Smith U.S. Pat. No. 2,887,112; Consentino U.S. Pat. No. 3,580,240; Berman U.S. Pat. No. 3,085,577; Maurer U.S. Pat. No. 3,817,252; McDonald U.S. Pat. No. 3,386,445; Corasanti U.S. Pat. No. 3,841,312 and Sarbacher U.S. Pat. No. 3,472,233. In addition, the prior art is thoroughly discussed in the aforementioned "Health Devices" magazine.
The aforementioned electrodes can be divided into disposable and reusable electrodes. The reusable grounding pad electrodes usually comprise a large metal plate made from lead, aluminum, or stainless steel. These electrodes suffer from numerous disadvantages. These plates are usually very large and rigid because of their thickness and hence do not conform very well to the body contact area. In addition, because the body contact area can be rounded, bony or have irregular body surfaces, only a small contact area may be presented to the large electrode, thereby resulting in burns. In addition, the body contact area may be reduced by the layers of sheets or surgical drapes being caught between the metal grounding plate and the patient before and during the surgical procedure. Finally, the plates require the body weight for contact and therefore must be under the body. Because of the body contour, there are only a few possible body locations at which these plate electrodes can be used and the patient must usually be moved in order to place the electrode which may be difficult because of the patient's condition or weight. It may also be difficult to ensure that the patient is in good contact with the electrode and that the patient remains in good contact therewith despite deliberate repositioning of the patient during the operation. In addition, the large plate electrodes may not be usable with pediatric or geriatric patients or patients having bony promiences or inadequate weight.
Reusable solid metal grounding plate electrodes, in general, have other disadvantages. The electrodes may become distorted, bent, and cracked with frequent use and thus provide less effective contact with the patient which may result in burns. Often the corners of the electrode will curl if the electrode is dropped or the electrode can be bent and distorted upon normal insertion and removal from beneath the patient. Occasionally tissue necrosis has occurred if the patient lies on a reusable electrode that has a bent edge or corner, which causes great pressure over a small area. In addition, the reusable electrode must be sanitized after each use, are usually large and inconvenient to store, and are usually expensive.
There are also available numerous types of disposable grounding pad electrodes, generally classifiable into the "plate-type" and the "adhesive-type". The plate-type disposable return electrodes are usually made of cardboard with a conductive foil coating or laminate on either one or both sides of the cardboard. The additional expense of putting foil on both sides of the cardboard has been justified to eliminate the possibility that the single sided cardboard will be placed under the patient with the wrong side (i.e., the cardboard side) against the patient. The adhesive-type disposable grounding pad electrodes normally comprise a conductive surface surrounded by an adhesive material. These electrodes can be placed around an arm or a leg and depend on adhesive, rather than the weight of the patient to hold them in place.
Disadvantages of the plate-type disposable grounding pad electrodes include splitting of the conductive surface after the electrode has been bent, curling and delamination if the cardboard backed electrodes become wet, are subjective to being torn, and the requirement to use an electrosurgical gel in order to assure good electrical contact with the skin. In addition to the foregoing, the conventional adhesive- type grounding adhesive-type have a generally smaller contact area and those which do not totally seal on the patient have a tendency to become wrinkled if not properly applied, have a tendency to lose their adhesive ability as a result of contact with fluids on or near the patient or snagging of the electrode, and must be applied around a curved area in order to keep enough uniform inward pressure on the pad for even current distribution. Furthermore, the use of both type electrodes often requires considerable retraining of the personnel who apply the electrodes to ensure proper application of the electrodes to the patient.
Many of the adhesive-type disposable grounding pad electrodes are also provided with a gel pad that is located in contact with the metal electrode and is placed against the patient's skin so as to assure a better electrical contact. One such electrode is disclosed in the aforementioned Patrick et al U.S. Pat. No. 3,848,600. The gel pad 32 disclosed therein is a very thick pad that is exposed to the air along its outer edge, thus allowing gel evaporation during long surgical procedures. The evaporation problem is exacerbated by the heating of the pad caused by the operating current. Gel pad drying results in increased contact impedance which in turn results in a greater gel pad temperature which further dries out the gel pad, and so forth.
Other difficulties experienced with prior art grounding pad electrodes include chemical reactions with aluminum electrodes with the resultant release of heat or caustic products and problems with cable connection to the electrode. The latter problem occasionally results in either the connecting cable coming loose or the coupling post attached to the metal plate working loose or, in multipiece posts, coming apart. The cable connection to the electrode assembly must be designed so as to withstand the flexure and strains of normal use. Numerous prior art electrode assemblies comprise a multipiece connecting post that is held in contact with the electrode plate by friction. This type of contact can result in a greater electrical impedance and is subject to being worked loose.